Yesterday, through tears and waves of raw emotion, Mr McLeod told of how his son Zaidok, aged 2, told him "I love you, daddy", during his last supervised visit on May 18.

Zaidok and Aaleyn, both six, Wyatt, four and Matilda, five, all died along with their mother Charmaine Harris McLeod when she hit an oncoming truck on the Bunya Highway, more than 200km west of Brisbane.

"Young Zaidoc - he was just a little adventurer. A loving and kind kid," Mr McLeod said of his youngest.

"The last supervised visitation I had with them, not last Saturday but the Saturday beforehand, he actually said that he loves me, daddy, to me. Just out of the blue.

"He was developing well and he was loved by all. Such an amazing little boy."

Mr McLeod also remembered his other children for their unique personalities.

"They were just beautiful souls mate. They were loved by everyone they were around, like at their daycare centres, their family, schools, Sunday schools, church.

"They were beautiful, intelligent, bright, smart kids.

"Each of them had their own character. They weren't all the same. Ally was the intelligent, smart, quiet one. She's also a leader. She was a leader in school. She helped guide kids in and adjust.

Charmaine McLeod and her four children were killed in a car crash near Kumbia on Monday night.

"Matilda was very handy with things - creative. She even used to help me work on my car. But she's a very fiery young girl and she used to keep busy all of the time doing anything."

He said his other son Wyatt was a "social butterfly" who provided the "glue" that kept young friends together at church and daycare.

"He just made anyone he met, he had no problems making friends with anyone and everyone. He just loved and accepted everybody."

Mr McLeod said "nobody - friends or rellies" knew why Ms Harris McLeod and the four children were driving in south-west Queensland.

The scene of the "catastrophic" crash near Kumbia on Monday night

"There's a lot of history to be honest. And we just want the police to do their job and to look into things and try to piece together what was actually happening," he said.

"Because nobody - no friends or rellies - had any idea what she was doing down there.

"We're just waiting. This is a real hard situation for us and it's just horrible.

"I don't want to assume anything. The police said just hang in there and be patient."

In Hervey Bay yesterday, a church-goer at Bayside Community Church said he was aware of mental health problems surrounding Ms Harris McLeod.

The man said she had sought counselling but there had been no sign of suicidal tendencies and she had a strong network of friends.

It is understood Mr McLeod and Ms Harris McLeod had been separated for more than a year.